Rotary mowers are well known for use in road-side maintenance, agriculture, and general grounds maintenance activities. Rotary mowers comprise a substantially horizontally oriented deck with a blade rotatably attached to a bottom side of the deck by a shaft extending through the deck to a blade gear box on top of the deck. The blade typically comprises a rotating blade bar or blade pan with blade knives pivotally attached thereto. A power shaft is connected to the input of the blade gear box to rotate the blade.
In many situations it is desirable to have as wide a mower as possible, for example for mowing large areas such as airports, agricultural fields, and the like. Thus mowers have thus been developed that have three decks comprising wings pivotally attached to a center section. This configuration provides improved ground following and a more even cut across the width of the mower compared to a wide rigid mower. A narrow transport width is provided as well by folding the wings up to a substantially vertical orientation along each side of the center section. In order to transport such a mower along roadways in many jurisdictions the transport width must be no greater than 3 meters. Height restrictions also often apply.
Such wing mowers typically include a single rotating blade on a center section, and the widest available mowers have two rotating blades on each wing. The blades are oriented typically in a V-configuration with the center blade nearest the front of the mower, the inner wing blade on each side slightly rearward of the center blade, and the outer wing blades slightly rearward of the inner wing blades. In order to provide some overlap to avoid misses, the rotational axes of one blade must be forward or rearward of the adjacent blades. It is also known to configure a three section mower with the center blade back near the rear of the mower, the inner wing blades forward, and the outer wing blades back again in a W-configuration.
A tractor towing the three section mower is connected by a power take off (pto) shaft to a main gear box, and then the main gear box typically has three outputs, each connected to a power shaft. A center power shaft is connected to a center gear box driving the center blade, and right and left power shafts are connected to corresponding right and left intermediate gear boxes driving the corresponding right and left inner wing blades, which intermediate gear boxes in turn each include another output connected to a power shaft driving an outer gear box and the outer blades.
The power shafts from the gear boxes typically include slip clutches to protect the drive train. Such slip clutches are designed such that when the blade strikes an obstruction, the clutch will slip and thus reduce damage to the drive train and the blade. The slip clutch will be set from the factory, or in some cases can be set in the field by tightening or loosening them, to transmit sufficient torque through the shaft to drive the blade during normal working conditions, but if the torque requirement climbs to a slipping point, such as when the blade hits a rock, the clutch will slip and the blade will stop. Typically the slipping point will be about 100% above the normal load to avoid constant slipping and poor cutting performance. On a typical mower the torque requirement during normal operations could be about 600 Newton-meters (NM), such that the slip clutch was set to slip at 1200 NM. Thus where the torque requirement on the shaft increases by 600 NM, the clutch will slip.
Typically the pto shaft from the tractor to the main gear box will not have a slip clutch, as the power shafts from the main gear box include slip clutches to provide the required protection. Thus the power shaft from the main gear box to the center gear box, and corresponding slip clutch, drives only the center blade, The power shafts from the main gear box to the right and left intermediate gear boxes, and corresponding slip clutches on each, are however required to drive both the inner and outer wing blades. Thus each slip clutch must be set to transmit sufficient torque through the shaft to drive two blades during normal operations.
For a typical mower the torque requirement during normal operations could be about 1200 Newton-meters (NM) for two blades, such that the slip clutch was set to slip at 2400 NM. Thus when one of the inner wing blades hits an obstruction, the torque requirement must climb by 1200 NM in order to cause the clutch to slip, reducing protection for the inner wing blade and drive line. The slip clutch can be loosened to reduce the torque at which same will slip, however there is then a risk of poor performance. The outer wing blade, like the center blade, is driven by a slip clutch on a shaft driving only that blade, so it is not affected by this problem.
Adding another blade outside the outer wing to make a wider mower would require adding an output to the outer gear box, and another power shaft to drive the outside blade. This would require that the power shafts from the main gear box to the right and left intermediate gear boxes, and corresponding slip clutches on each, drive the inner, outer, and outside blades, or three blades, exacerbating the problem significantly.
Other types of protection could be provided, such as providing a slip clutch in the short drive shaft down from each gear box to the blade being driven, however slip clutches are preferred for reasons of economy, convenience, and the like, and the reduced protection is not prohibitive in a three section mower, affecting only the inner wing blades.
Such mowers have been limited in width to about 8.5 meters. The width of the center section is limited by the transport width, and height restrictions limit the overall length of the wings which upward from the sides of the center section. Stability issues arise as well when the upright wings are excessively high.
Other towed implements, such as agricultural ground working implements such as cultivators and the like, have been extended to wider widths by adding outer wings to the inner wings to create a five section implement. This is relatively straightforward with implements that do not require a mechanical rotating drive train out to the outside wings. Where such a drive train is required as is the case for rotary mowers, significant problems arise in providing a suitable drive train that can power the outside rotor, provide satisfactory driveline protection, and at the same time fold into a satisfactory transport width.